Undefines the value of
EXPR, which must be an lvalue. Use only on a scalar value, an entire array, an entire hash, or a subroutine name (using ``&''). (Using undef() will probably not do what you expect on most predefined variables or
DBM list values, so don't do that.) Always returns the undefined value. You can omit the
EXPR, in which case nothing is undefined, but you still get an undefined value that you could, for instance, return from a subroutine, assign to a variable or pass as a parameter. Examples: